Modular physiological sensor

ABSTRACT

Modular physiological sensors that are physically and/or electrically configured to share a measurement site for the comfort of the patient and/or to ensure proper operation of the sensors without interference from the other sensors. The modular aspect is realized by providing outer housing shapes that generally conform to other physiological sensors; mounting areas for attachment of one sensor to another sensor; providing release liners on the overlapping sensor attachment areas; and/or providing notches, tabs or other mechanical features that provide for the proper placement and interaction of the sensors.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

The present application is a continuation of U.S. patent applicationSer. No. 16/182,388 filed Nov. 6, 2018, which is a continuation of U.S.patent application Ser. No. 14/876,307 filed Oct. 6, 2015, now U.S. Pat.No. 10,154,815, which claims priority benefit under 35 U.S.C. § 119(e)to U.S. Provisional Patent Application Ser. No. 62/061,132 filed Oct. 7,2014, titled Regional Oximetry-EEG Sensor. The above-cited provisionalpatent application is hereby incorporated in its entirety by referenceherein.

FIELD OF THE DISCLOSURE

The present disclosure relates to physiological sensors. Morespecifically, the present disclosure relates to configurations formodular physiological sensors.

BACKGROUND

Pulse oximetry is a widely accepted noninvasive procedure for measuringthe oxygen saturation level of arterial blood, an indicator of aperson's oxygen supply. A typical pulse oximetry system utilizes anoptical sensor attached to a fingertip to measure the relative volume ofoxygenated hemoglobin in pulsatile arterial blood flowing within thefingertip. Oxygen saturation (SpO2), pulse rate and a plethysmographwaveform, which is a visualization of pulsatile blood flow over time,are displayed on a monitor accordingly.

Conventional pulse oximetry assumes that arterial blood is the onlypulsatile blood flow in the measurement site. During patient motion,venous blood also moves, which causes errors in conventional pulseoximetry. Advanced pulse oximetry processes the venous blood signal soas to report true arterial oxygen saturation and pulse rate underconditions of patient movement. Advanced pulse oximetry also functionsunder conditions of low perfusion (small signal amplitude), intenseambient light (artificial or sunlight) and electrosurgical instrumentinterference, which are scenarios where conventional pulse oximetrytends to fail.

Advanced pulse oximetry is described in at least U.S. Pat. Nos.6,770,028; 6,658,276; 6,157,850; 6,002,952; 5,769,785 and 5,758,644,which are assigned to Masimo Corporation (“Masimo”) of Irvine,California and are incorporated in their entireties by reference herein.Corresponding low noise optical sensors are disclosed in at least U.S.Pat. Nos. 6,985,764; 6,813,511; 6,792,300; 6,256,523; 6,088,607;5,782,757 and 5,638,818, which are also assigned to Masimo and are alsoincorporated in their entireties by reference herein. Advanced pulseoximetry systems including Masimo SET® low noise optical sensors andread through motion pulse oximetry monitors for measuring SpO2, pulserate (PR) and perfusion index (PI) are available from Masimo. Opticalsensors include any of Masimo LNOP®, LNCS®, SofTouch™ and Blue™ adhesiveor reusable sensors. Pulse oximetry monitors include any of Masimo Rad8®, Rad 50, Rad®-5v or SatShare® monitors.

Advanced blood parameter measurement systems are described in at leastU.S. Pat. No. 7,647,083, filed Mar. 1, 2006, titled Multiple WavelengthSensor Equalization; U.S. Pat. No. 7,729,733, filed Mar. 1, 2006, titledConfigurable Physiological Measurement System; U.S. Pat. Pub. No.2006/0211925, filed Mar. 1, 2006, titled Physiological ParameterConfidence Measure and U.S. Pat. Pub. No. 2006/0238358, filed Mar. 1,2006, titled Noninvasive Multi-Parameter Patient Monitor, all assignedto Cercacor Laboratories, Inc., Irvine, Calif. (Cercacor) and allincorporated in their entireties by reference herein. Advanced bloodparameter measurement systems include Masimo Rainbow® SET, whichprovides measurements in addition to SpO2, such as total hemoglobin(SpHb™), oxygen content (SpOC™), methemoglobin (SpMet®),carboxyhemoglobin (SpCO®) and PVI®. Advanced blood parameter sensorsinclude Masimo Rainbow® adhesive, ReSposable™ and reusable sensors.Advanced blood parameter monitors include Masimo Radical-7™, Rad-87™ andRad-57™ monitors, all available from Masimo. Such advanced pulseoximeters, low noise sensors and advanced blood parameter systems havegained rapid acceptance in a wide variety of medical applications,including surgical wards, intensive care and neonatal units, generalwards, home care, physical training, and virtually all types ofmonitoring scenarios.

SUMMARY

The present disclosure relates to modular physiological sensors. In somesituations in the clinical environment, it is necessary to use multiplephysiological sensors in the same general measurement site of a patient.For example, the forehead, arm, hand, ear, and noes are all common areaswhere multiple physiological sensors may be used at the same time. Thepresent disclosure provides for modular physiological sensors that arephysically and/or electrically configured to share the measurement sitefor the comfort of the patient and to ensure proper operation of thesensors without interference from other sensors. The modular aspect isrealized by providing outer housing shapes that generally conform toother physiological sensors; mounting areas for attachment of one sensorto another sensor; providing release liners on the overlapping sensorattachment areas; and/or providing notches, tabs or other mechanicalfeatures that provide for the proper placement and interaction of thesensors.

For example, regional oximetry (rO2), also referred to as tissueoximetry and cerebral oximetry, enables the continuous assessment oftissue oxygenation beneath a regional oximetry optical sensor. Regionaloximetry helps clinicians detect regional hypoxemia that pulse oximetryalone can miss. In addition, the pulse oximetry capability in regionaloximetry sensors can automate a differential analysis of regional tocentral oxygen saturation. Regional oximetry monitoring is as simple asapplying regional oximetry sensors to any of various body sitesincluding the forehead, forearms, chest, upper thigh, upper calf orcalf, to name a few. Up to four sensors are connected to a conventionalpatient monitor via one or two regional oximetry pods. The podsadvantageously drive the sensor optics, receive the detected opticalsignals, perform signal processing on the detected signals to deriveregional oximetry parameters and communicate those parameters to aconventional patient monitor through, for example, standard USB ports.Although much of the present disclosure is explained by way of examplewith respect to EEG and rO2 sensors, it is to be understood that themodular configurations of the sensors can be applied to other types ofphysiological sensors and are not limited to EEG and rO2 sensors.

In some embodiments, an EEG sensor is advantageously shaped and markedon either side of a connector stem so as to allow regional oximetry(rO2) sensors to be placed in close proximity to the EEG sensor and soas to guide the proper placement of one or more rO2 sensors compactlynext to the EEG sensor. The proper placement assistance and jointoperation of the sensors provides for improved patient comfort andimproved monitoring by ensuring the sensors do not interfere with eachother. In some embodiments, the body shape of the EEG sensor is designedto the egg-shaped contours of the rO2 sensor heads. Further, markings onEEG contours correspond to notches on the rO2 sensor heads. Thesenotches allow the rO2 sensor heads to conform to the curvature of aperson's forehead. This integrated rO2-EEG sensor combination allows formeasuring cerebral regional oximetry in conjunction with EEG parameters,such as depth of consciousness. The EEG sensor is applied first, as theEEG sensor electrodes have particular placement criteria. The EEG sensormarkings, as described above, guide placement of the rO2 sensors, asthese too require a particular placement for cerebral regional oximetrymeasurements. The EEG sensor skin-side is advantageously colored blackso as to prevent the EEG sensor from reflecting the rO2 sensor-emittedlight into the sensor detectors, which would degrade rO2 sensorperformance.

In some embodiments, the rO2 sensors connect with a single rO2 pod andcable and the EEG sensor connects with a separate EEG pod and cable. Invarious other embodiments, a combination rO2-EEG sensor pod houses asingle rO2 analog/digital signal processing board and a single EEGsignal processing board and the rO2-EEG sensors each connect to thesingle rO2-EEG sensor pod.

One aspect of a brain analysis sensor is an EEG sensor having a stem, aleft branch and a right branch. The left branch and the right branchextend generally perpendicularly from the stem so as to form a branchintersection. A plurality of right and left active electrodes aredisposed along the left branch and the right branch. A ground electrodeand reference electrode are disposed proximate the branch intersection.A mounting zone is disposed proximate the branch intersection forremovable attachment of at least one regional oximetry (rO2) sensor.

In various embodiments, the mounting zone accommodates a regionaloximetry sensor head having light emitting and light detecting elements.The mounting zone is marked with a curved line generally indicating ashape of the regional oximetry sensor head. The mounting zone comprisesa release layer so that the regional oximetry sensor head removablyattaches to the mounting zone. The regional oximetry sensor head hasnotches that accommodate a curved surface and the mounting zone hasnotch markings that generally align with the sensor head notches so asto aid regional oximetry sensor placement. The mounting zone isconfigured to removably attach two regional oximetry sensor heads. Afirst regional oximetry sensor head is mounted proximate a EEG sensorleft branch and a second regional oximetry sensor head is mountedproximate a EEG sensor right branch.\

Another aspect of a brain analysis sensor is a sensor method comprisingmounting an EEG sensor on a forehead tissue site, mounting a firstregional oximetry sensor on the forehead tissue site so as to at leastpartially overlap a first portion of the EEG sensor and mounting asecond regional oximetry sensor on the forehead tissue site so as to atleast partially overlap a second portion of the EEG sensor.

In various embodiments, the first portion and the second portion of theEEG sensor are marked for placement of the first and second regionaloximetry sensors. A release liner is disposed on the first portion andthe second portion for aiding removal of the regional oximetry sensors.The shape of the marked portions conform to shape of the regionaloximetry sensors. The marked portions also designate the location ofnotches on head portions of the regional oximetry sensors.

A further aspect of a brain analysis sensor is an electrical sensormeans for passively measuring an EEG signal, an optical sensor means fordetecting an oxygen saturation and a placement means for at leastpartial overlapping the electrical sensor means and the optical sensormeans on a tissue site. In an embodiment, the placement means comprisesa marking means for designating the partial overlapping. In anembodiment, the marking means comprises at least a partial duplicationof the optical sensor means shape on the electrical sensor means.

Regional oximetry sensors and pods are disclosed in U.S. patentapplication Ser. No. 14/507,620, titled Regional Oximetry Sensor, filedOct. 6, 2014 by Masimo Corporation, Irvine, Calif. and incorporated inits entirety by reference herein. An EEG sensor and monitor aredisclosed in U.S. patent application Ser. No. 14/470,819, titled Depthof Consciousness Monitor, filed Aug. 27, 2014 by Masimo Corporation,Irvine, Calif. and incorporated in its entirety by reference herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a brain analysis system having anadvantageous modular brain analysis sensor applied to a forehead siteand in communications with a physiological monitor for generatingsimultaneous electroencephalogram (EEG) and left and right foreheadregional oximetry (rO2) parameter values and waveforms;

FIGS. 2-3 are perspective views, respectively, of a regional oximetry(rO2) sensor and cable assembly and an EEG sensor and cable assembly;

FIGS. 4A-B are an exploded plan view (FIG. 4A) and a detailed plan view(FIG. 4B), respectively, of a modular brain analysis sensor having anadvantageous keyed mounting zone (shaded) for precise, overlaidplacement of dual rO2 sensors on an rO2-configured EEG sensor;

FIGS. 5A-E are top, perspective, bottom, side and exploded perspectiveviews, respectively, of an rO2-configured EEG sensor; and

FIGS. 6A-E are top, side, bottom and exploded top perspective views,respectively, of a rO2 sensor and an enlarged perspective view of rO2sensor optical elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a brain analysis system 100 having an advantageousmodular brain analysis sensor 400 applied to a forehead tissue site incommunications with a physiological monitor 101 for measuring andgenerating simultaneous electroencephalogram (EEG) and left and rightforehead regional oximetry (rO2) parameter values and waveforms. Themodular brain analysis sensor 400 can be advantageously assembled andplaced within a limited-area forehead site. Also, the rO2 components 600and EEG component 500 can be advantageously purchased, stocked and usedseparately and individually, saving hospital and medical care centercosts over other, more specialized brain analysis sensors not havingseparately useable regional oximetry and EEG sensor functions. The samecost savings is realized by modular designs for any and all types ofphysiological monitoring sensors.

As shown in FIG. 1, the brain analysis sensor 400 has an EEG sensor(FIGS. 4-5) that co-mounts dual regional oximetry (rO2) sensors. Each ofthese sensor functions are in communications with a physiologicalmonitor 101 having a main display 120 and a (removable) handheld monitor130 having a handheld display 132. The main display 120 provides EEGwaveforms and parameter values 122 in addition to forehead left 124 andforehead right 125 regional oximeter waveforms and parameters. Thehandheld display 132 provides a 3-D man graphic displaying green, yellowand red organ symbols (brain, lung and kidneys) corresponding to EEGand/or rO2 parameter values. Similar displays can be provided for otherphysiological parameters as well.

Also shown in FIG. 1, a modular brain analysis sensor 400 advantageouslyhas dual rO2 sensors 600 that overlap right- and left-side portions of aspecially-configured and marked (rO2-configured) EEG sensor 500 so as tocompactly fit these modular sensors 500, 600 within a limited-spaceforehead site, as described in detail with respect to FIGS. 2-4, below.An rO2-configured EEG sensor 500 is described in detail with respect toFIGS. 5A-E, below. An regional oximetry sensor 600 is described indetail with respect to FIGS. 6A-E, below.

Further shown in FIG. 1, in an EEG screen portion 122, the physiologicalmonitor 101 display 120 shows 4 simultaneous EEG channels along with apatient state index (PSI) readout versus time so as to enable continuousassessment of both sides of the brain, such as for improved anestheticmanagement. In addition, forehead left 124 and forehead right 125regional oximetry waveforms and readouts enable monitoring of braintissue oxygen saturation and detect regional hypoxemia.

FIGS. 2-3 illustrate, respectively, a regional oximetry (rO2) sensor andcable assembly and an EEG sensor and cable assembly. As shown in FIG. 2,the regional oximetry (rO2) cable assembly 200 interconnects dual rO2sensors 600 to a physiological monitor 101 (FIG. 1). The rO2 cableassembly has dual sensor connectors at a sensor end, a monitor connector(MOC9) at a monitor end and a rO2 pod mounted between and incommunications with the sensor connectors and the monitor connector.Also shown in FIG. 2, the rO2 pod has regional oximetry analog anddigital boards. The analog board communicates with one or more of theregional oximetry sensors 600. The digital board enables the pod toperform the sensor communications and signal processing functions of aconventional patient monitor. This allows pod-derived regional oximetryparameters to be displayed on a variety of monitors ranging from simpledisplay devices to complex multiple parameter patient monitoringsystems.

As shown in FIG. 3, the EEG cable assembly 300 interconnects an EEGsensor 500 to a physiological monitor 101 (FIG. 1). The EEG cableassembly 300 has an EEG connector at a sensor end, a monitor connector(MOC9) at a monitor end and a EEG pod mounted between and incommunications with the sensor connectors and the monitor connector.

FIGS. 4A-B illustrate a modular brain analysis sensor 400 havingadvantageous keyed mounting zones 501 (shaded) for precise, overlaidplacement of dual rO2 sensors on an EEG sensor. In particular, the EEGsensor 500 has two mounting zones 501, one on either side of theinterconnected between the EEG electrodes and the EEG sensor connector.Each mounting zone accommodates one of two rO2 sensors (see FIG. 1 andFIG. 4A). Further, each mounting zone 501 (FIG. 4B) is shaped andprinted to conform to a top and side portion of an rO2 sensor head 610(FIGS. 6A-D). Further, each mounting zone has printed notches 502, 504corresponding to actual notches in the rO2 sensor heads 610 (FIG. 6A)that accommodate curved tissue site surfaces. These printed notches 502,504 further aid in the alignment of rO2 sensors to the mounting zones501.

FIGS. 5A-E further illustrate an rO2 configured EEG sensor 500 having agenerally “T” shape with six electrodes including two right electrodesR1, R2; two left electrodes L1, L2; a ground electrode CB and areference electrode CT. As shown in FIG. 5A, the R1, R2, L1, L2 and CBelectrodes are disposed across the horizontal top of the “T.” Thereference electrode CT is disposed on the vertical middle of the “T.”The advantageous mounting zone 501 (FIG. 4B) is disposed on either sideof the vertical middle of the “T” proximate the horizontal top of the“T.”

As shown in FIG. 5E, the EEG sensor 500 has multiple layers including arelease liner 510 that allows an attached rO2 sensor 600 (FIG. 1) to beremoved and repositioned; artwork 520 including rO2 sensor positioninglines 502 (FIG. 4B); a polyester substrate 530; silver pads 540(electrodes); silver ink traces 550; a dielectric layer 560 thatisolates and protects the traces 550 and a foam pad 570 that contacts auser's skin. The EEG sensor connector includes a top shell 582 and abottom shell 584. An information element 585 mechanically andelectrically connects to the trace layer 550.

FIGS. 6A-E further illustrate a rO2 sensor and its optical elementshaving a sensor head 610, a stem 620 and a connector 630. The sensorhead 610 houses an emitter 682, a near-field detector 684 and afar-field detector 688 within a layered tape having a top side (FIG. 6A)and an adhesive bottom side (FIG. 6C) disposed on a release liner. Therelease liner is removed so as to adhere the bottom side to a skinsurface. The emitter 682 and detectors 684,688 have lens that protrudefrom the bottom side (FIG. 6E) advantageously providing a robustoptics-skin interface. The top side has printed emitter/detectorindicators so as to aid precise sensor placement on a patient site. Aconnector 630 terminates the interconnect 620 at the connector contacts632.

Also shown in FIG. 6D, a sensor head assembly 610 has a face tape 612, aflex circuit 622, a stem tape 620, a base tape 624, a connector top 634and a connector base 636. The face tape 612 and base tape 622 encase theflex circuit 622 and corresponding emitter and detectors 682-688.

A modular physiological sensor has been disclosed in detail inconnection with various embodiments. These embodiments are disclosed byway of examples only and are not to limit the scope of this disclosureand the claims herein. One of ordinary skill in art will appreciate manyvariations and modifications. It should be understood specifically thatthe present mounting zones, tabs, relative shapes and modularconfiguration can be applied to other physiological sensors including,for example, ear, nose, hand, harm, and/or chest sensors or any othertypes of physiological sensors where the sensors are configured tojointly measure the same measurement site of a patient.

What is claimed is:
 1. An electroencephalogram (EEG) sensor comprising:a stem; a left branch; a right branch, wherein the left branch and theright branch extend generally perpendicularly from the stem in oppositedirections so as to form a branch intersection, wherein the branchintersection includes a left corner defined by an intersection of theleft branch and the stem and a right corner defined by an intersectionof the right branch and the stem; a first plurality of EEG electrodesdisposed along the left branch; a second plurality of EEG electrodesdisposed along the right branch; a ground electrode and a referenceelectrode, the ground and reference electrodes disposed proximate thebranch intersection; a first mounting zone extending along the leftcorner of the branch intersection, a first portion of the stem, and aportion of the left branch proximate one of the first plurality of EEGelectrodes, the first mounting zone comprising a release layerconfigured to allow an adhesive portion of a first regional oximetry(rO2) sensor to removably attach on top of the first mounting zone; anda second mounting zone extending along the right corner of the branchintersection, a second portion of the stem, and a portion of the rightbranch proximate one of the second plurality of EEG electrodes, thesecond mounting zone comprising a release layer configured to allow anadhesive portion of a second regional oximetry (rO2) sensor to removablyattach on top of the second mounting zone; wherein the second portion ofthe stem is spaced from the first portion of the stem; and wherein thereference electrode is positioned between the first and second portionsof the stem.
 2. The EEG sensor according to claim 1, wherein the groundelectrode and the reference electrode are aligned with an axis extendingalong a length of the stem of the EEG sensor.
 3. The EEG sensoraccording to claim 1, wherein the first plurality of EEG electrodesdisposed along the left branch comprises two electrodes.
 4. The EEGsensor according to claim 3, wherein the second plurality of EEGelectrodes disposed along the right branch comprises two electrodes. 5.The EEG sensor according to claim 1, wherein a skin-side surface of theEEG sensor is colored black.
 6. The EEG sensor according to claim 1,wherein the first mounting zone comprises a first positioning lineconfigured to aid attachment of the adhesive portion of the first rO2sensor, and wherein the second mounting zone comprises a secondpositioning line configured to aid attachment of the adhesive portion ofthe second rO2 sensor.
 7. The EEG sensor according to claim 1, whereinan edge of the left corner of the branch intersection has a firstcurvature and an edge of the right corner of the branch intersection hasa second curvature which matches the first curvature.
 8. Anelectroencephalogram (EEG) sensor comprising: a stem; a left branch; aright branch, wherein the left branch and the right branch extendgenerally perpendicularly from the stem in opposite directions so as toform a branch intersection, wherein the branch intersection includes aleft corner defined by an intersection of the left branch and the stemand a right corner defined by an intersection of the right branch andthe stem; one or more EEG electrodes disposed along the left branch; oneor more EEG electrodes disposed along the right branch; a groundelectrode and a reference electrode; a first mounting zone extendingalong the left corner of the branch intersection, a first portion of thestem, and a portion of the left branch proximate one of the one or moreEEG electrodes disposed along the left branch, the first mounting zonecomprising a release layer configured to allow an adhesive portion of afirst regional oximetry (rO2) sensor to removably attach on top of thefirst mounting zone; and a second mounting zone extending along theright corner of the branch intersection, a second portion of the stem,and a portion of the right branch proximate one of the one or more EEGelectrodes disposed along the right branch, the second mounting zonecomprising a release layer configured to allow an adhesive portion of asecond regional oximetry (rO2) sensor to removably attach on top of thesecond mounting zone; and wherein the second portion of the stem isspaced from the first portion of the stem.
 9. The EEG sensor accordingto claim 8, wherein the ground electrode and the reference electrode arepositioned proximate the branch intersection and are aligned with anaxis extending along a length of the stem of the EEG sensor.
 10. The EEGsensor according to claim 8, wherein the one or more EEG electrodesdisposed along the left branch comprises two electrodes.
 11. The EEGsensor according to claim 10, wherein the one or more EEG electrodesdisposed along the right branch comprises two electrodes.
 12. The EEGsensor according to claim 8, wherein the reference electrode ispositioned between the first and second portions of the stem.
 13. TheEEG sensor according to claim 8, wherein the first mounting zonecomprises a first positioning line configured to aid attachment of theadhesive portion of the first rO2 sensor, and wherein the secondmounting zone comprises a second positioning line configured to aidattachment of the adhesive portion of the second rO2 sensor.
 14. The EEGsensor according to claim 8, wherein an edge of the left corner of thebranch intersection has a first curvature and an edge of the rightcorner of the branch intersection has a second curvature which matchesthe first curvature.
 15. An electroencephalogram (EEG) sensorcomprising: a stem; a left branch; a right branch, wherein the leftbranch and the right branch extend from the stem in opposite directionsso as to form a branch intersection, wherein the branch intersectionincludes a left corner defined by an intersection of the left branch andthe stem and a right corner defined by an intersection of the rightbranch and the stem; one or more EEG electrodes disposed along the leftbranch; one or more EEG electrodes disposed along the right branch; aground electrode and a reference electrode; a first mounting zoneextending along the left corner of the branch intersection, a firstportion of the stem, and a portion of the left branch proximate one ofthe one or more EEG electrodes disposed along the left branch, the firstmounting zone configured to allow an adhesive portion of a firstregional oximetry (rO2) sensor to removably attach on top of the firstmounting zone; and a second mounting zone extending along the rightcorner of the branch intersection, a second portion of the stem, and aportion of the right branch proximate one of the one or more EEGelectrodes disposed along the right branch, the second mounting zoneconfigured to allow an adhesive portion of a second regional oximetry(rO2) sensor to removably attach on top of the second mounting zone. 16.The EEG sensor according to claim 15, wherein the ground electrode andthe reference electrode are positioned proximate the branch intersectionand are aligned with an axis extending along a length of the stem of theEEG sensor.
 17. The EEG sensor according to claim 15, wherein the one ormore EEG electrodes disposed along the left branch comprises twoelectrodes, and wherein the one or more EEG electrodes disposed alongthe right branch comprises two electrodes.
 18. The EEG sensor accordingto claim 15, wherein the left and right branches extend perpendicularlyfrom the stem of the EEG sensor in opposite directions.
 19. The EEGsensor according to claim 10, wherein the second portion of the stem isspaced from the first portion of the stem.
 20. The EEG sensor accordingto claim 19, wherein the reference electrode is positioned between thefirst and second portions of the stem.